Re: [Postgres-xc-developers] GTM/GTM Proxy invalid handles and failed to get snapshot issues

[Ashutosh B. <ash...@en...>]

Sorry, I wasn't clear enough.

Can GTM/proxy cleanup the pending list when it detects the death of a
connection, just like GTM does its cleanup?


On Tue, Aug 6, 2013 at 11:03 AM, Nikhil Sontakke <ni...@st...>wrote:

>
> A naive question,
>> Can we also cleanup the pending list?
>>
>>
> Umm, the processed commands are put onto the thr_processed_commands list
> and freed up eventually. Is that what you were asking?
>
> Regards,
> Nikhils
>
>>
>>  On Tue, Aug 6, 2013 at 9:56 AM, Nikhil Sontakke <ni...@st...>wrote:
>>
>>> Hi,
>>>
>>> We have had a long standing issue with a GTM Proxy in the mix. It has
>>> been reported here:
>>>
>>>
>>> http://sourceforge.net/mailarchive/forum.php?thread_name=CAB7nPqQ51fabopxCOHPrRM%3D2WTJMikfZUPHNEW942DDHmED7bQ%40mail.gmail.com&forum_name=postgres-xc-developers
>>>
>>> I think I found the root cause:
>>>
>>> Here's how things work:
>>>
>>> The client connects to proxy. The proxy internally connects to the GTM.
>>>
>>> Some commands from clients are sent immediately to the GTM by the proxy.
>>>
>>> Some commands are put in the pending list on the proxy for batch
>>> processing later.
>>>
>>> Now, if the client goes away before processing pending commands, the
>>> proxy is immediately telling the GTM so. That initiates a cleanup on the
>>> GTM side and removes the XIDs associated with this client. After this
>>> cleanup when the GTM receives a command like "MSG_SNAPSHOT_GET" or
>>> "MSG_TXN_COMMIT_MULTI" etc. from the pending list from the proxy, then it's
>>> going to get confused.
>>>
>>> A way to handle this is to put "disconnected" messages also onto the
>>> pending list. We then process these "disconnected" messages LAST from the
>>> pending list.
>>>
>>> I have tried this fix and run a number of tests (using pgbench) and
>>> things seem to be ok. I do not see the invalid handle and snapshot errors
>>> on the GTM side with this patch in place.
>>>
>>> PFA, patches for 1.0, 1.1 and head attached with this email.
>>>
>>> Regards,
>>> Nikhils
>>> --
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>>>
>>
>>
>> --
>> Best Wishes,
>> Ashutosh Bapat
>> EntepriseDB Corporation
>> The Postgres Database Company
>>
>
>
>
> --
> StormDB - http://www.stormdb.com
> The Database Cloud
>



-- 
Best Wishes,
Ashutosh Bapat
EntepriseDB Corporation
The Postgres Database Company